1/8teaspoonground black pepperplus additional to taste
Prep the steak: With paper towels, pat the steak dry. Place in a large ziptop bag or large bowl, with the salt, pepper, balsamic vinegar, and oil. Seal the bag (if using), removing as much air as possible. Turn to coat the steak. Set aside at room temperature for 30 minutes, or refrigerate overnight.
Meanwhile, cut the onion into 1/2-inch thick rings. Lightly brush each side with olive oil. Cut the cherry tomatoes in half.
Make the dressing: In a medium bowl or large measuring cup, whisk together the balsamic, oil, Dijon, honey, salt, and pepper.
Cook the steak and onion: Heat the grill over medium-high heat (425 to 450 degrees F) or heat the oven’s broiler. If using the broiler, line a rimmed baking pan with foil. Remove the steak from the marinade, allowing as much excess marinade as possible to drip away. Grill or broil the onion and steak, until the steak is medium-rare and the onion is charred on both sides—3 to 4 minutes per side depending on its thickness, until the steak reaches 130 degrees F on an instant read thermometer. (If you like your steak more well done, cook it 1 to 2 minutes more, but note that it will be tough).
Place the steak on a cutting board and let rest at least 5 minutes.
In a large bowl, place the mixed greens, arugula, halved tomatoes, half of the cheese, and the grilled onions (separate the rings as you add them).
Add enough dressing over the top to moisten, then toss to coat. Divide the salad between individual plates, or place in the center of a large serving plate.
VERY thinly slice the steak across the grain (about 1/4-inch wide). Serve on top of or alongside the salad. Sprinkle on the remaining blue cheese. Enjoy!
*Nutrition has been calculated with only half of the dressing and without the marinade, as it is discarded.
TO STORE: Refrigerate leftover salad in an airtight storage container for up to 3 days. If possible, store the steak, salad, and dressing separately.
TO REHEAT: Gently rewarm steak in a skillet on the stovetop over medium-low heat or in the microwave.
TO FREEZE: Leftover steak can be frozen in an airtight, freezer-safe storage container for up to 3 months. Let thaw overnight in the refrigerator before reheating.